Process for metalizing nonmetallic articles



Patented Aug. 17 1943 FROCESS FOR METALIZING NONMETALLIC ARTICLESFrederick Ross Wenger, Los Angeles, Calif., as- Signor to Focal Company,Downey, Califl, a corporation of California I No Drawing.Application'April 21, 1943, Serial No. 483,948

- 1 Claims. (Cl. inc-47) This invention relates to a process for themetalizationof plastics and other non-metallic substances, such aspaper, Celluloid, sheet cork,

fivory, bone, hard rubber, wood, leather, cloth,

horn, pressed Woods, imitation leather, glass,

porcelain products and plastic materials which are not reactive toalcohols, ketones and esters,

and the products resulting therefrom,

It has heretofore been proposed to coat nonmetallic substances withmetal, such as silver or copper, but these processes have not beenentirely satisfactory due to cost, time consumed in treating thesubstance to be metalized, and lack ing the non-metallic substance, orarticle to be metalized, to three baths to be specified hereinafter, andthen a platin operation of any Wellknown type now'in use. As one exampleof cardipped in the following. solution to oxidize the silver depositedon the sheet'i'n the firstdip:

To equal parts of water and denatured ethyl alcohol byv volume add 5 or10% of alight metal hydroxide, such as sodium hydroxide or potassiumhydroxide. The denatured alcohol content of this solution .should. notdrop below 50%. When the hydroxide is added, the solution will turn anamber color. The solution should be allowed to age for at least 24h0ursbefore using. The treated sheet of plastic is now given a thirty seconddip in this oxidizing solution at room temperature whereupon thesolution oxidizes the silver on the sheet converting it. toeither silverhydroxide or silver oxide. If a. heavier coating is desired thesheet maybeleft in thesolution for or 50 seconds. Itis then dried and'is readyfora reducing bath.

In order to prepare the reducing bath a select- .ed quantity of water issaturated with sulfurdioxide gas to, obtain sulphurous acid,

rying out the novel process, the same will be j' described, merely forthe purpose of illustration, .in' connection'with the metalization ofplastics cellulose'nitrates, and cellulose acetates and plastics whichdo not react to alcohols, ketones and;

esters.

A plain, clean sheet of cellulose nitrate plastic is first subjected toabath of acetone, denatured alcohol and silver nitrate. This bath orsolution is formed by dissolving silver nitrate crystals in, 1 denaturedalcohol at a temperature of approximately 15 C'.,'or"slig'h't1y higher,and this mixture is added to acetone. Preferably the bath comprises 50parts by volume of denatured ethyl alcohol, 50 parts by volume ofacetone and silver nitrate crystals of from 5 to 10 parts of the mixtureof acetone and alcohol. Nothing is gained by adding more than 10 partsby volume of silver nitrate although if an alcohol of a higher specificgravity is used a greater amount of silver nitrate crystals will bedissolved. The best results have been obtained by using ethyl alcohol inthe bath where methyl alcohol or acetone is used as the denaturant. Theplastic sheet is dipped into the bath at room temperature, 1. e.,approximately 65 F., for thirty seconds and after this dip the articleis dried, preferably in a stream of warm air.

After the initial silver dip, the plastic sheet is Sodium sulphite isnow added to the sulphurous acid until the reaction of the acid ceases.

.There isthus obtained a saturate solution of so- 1 to c. c. of thestock solutionof sodium bisulphite is added 500 c. c. of water and intothis is poured powdered zinc to obtain the following reaction:

This mixture is kept cool as by means of ice or cold water until thereaction between the zinc and the acid of the bisulphite has beencompleted. A portion of the zinc sulphite is converted into a basic saltand S02, thus set free, is then reduced in turn by the excessive zincpresent. A reducing bath thus formed gives fair results if used within afew hours after it is first made but better results silver finish. Thestrip can then be plated with any suitable material, such as copper,where the required temperature of the plating bath is below the dangerpoint of deterioration of the plastic base.

The-reducing. bath slowly oxidizes and hence must be' kept in a closedcontainer. It has been found that if a small amount of sugar, honey, orglycerine is added, the oxidation will be slowed and the keepingproperties improved. It is noted that meta bisulphite should not be usedin making the reducing bath because if used sulphides will be formed andthe results" willbe unsatisfactory.

When metalizing the other non-metallic substances referred to above,such as rubber, for 'example, it is preferred to make a solution of acellulose nitrate plastic and acetone to the consistency of light cream.The rubber, Or other article, is dipped into this cream, then dried andprocessedin accordance with the procedure outlined v above for thecellulose nitrates strip.

'Therejis "thus" provided a novel and simple "niethod for metalizingnon-metallic substances *and'one Whichcan be quickly and inexpensively"carried out. and has awi'de variety of uses as will be apparent tothose skilled in the art.

Theproduct obtained is durable fWl'iat is claimed is: "1. A process formetalizing non-metallic arti- "cles ofthe class described-which includesthe steps" of "subjecting the article to a bath of de- "'n'aturedalcohol; acetone and silver nitrate, dry- "ingiand subjecting thearticle to a bath of'water, denatured alcohol andan alkalimetalihydroxide,

' and'd'rylngand subjectingthe article to a reducingbeithof sodiumbisulphite andzinc.

2. A process for metalizing non metallic articlesof the class describedwhich includes the steps of treating the article with r a silver nitratesolution, subjecting the treated article to alcohol, metal hydroxideoxidation of the silver deposited thereon -from= the first s01uti0n,-andsubjecting to :convert the :oxidized silver to metallic silver.

A process for-metalizing non-"metallic articles of theclass -describedwhich consists in sub- :je ctingethe article toa silvernitrate-denatured alcohol-and an alkali metalhydroxida. drying thearticle,.i dipping the dried article in abath of sodium bisulphite and.zinc, and r washinguand drying the article.

4. A process for metalizing non-metallic arti cles..of :the classdescribed which includesthe the article toa solution containing zincsulphite steps of subjecting the article to a silver nitrate denaturedalcohol-acetone bath, drying the article and subjecting it to anoxidizing bath of denatured alcohol, water and sodium hydroxide, dryingthe article and subjecting it to a bath formed by introducing powderedzinc into sodium bisulphite.

5. A process for metalizing a plastic article which consists in dippingthe plastic article in a silver nitrate-denatured ethyl alcohol-acetonebath, drying the article, subjecting the dried article to a bath ofwater, denatured ethyl alcohol and sodium hydroxide, drying the article,dipping the driedarticle in a bath of sodium bisulphite and zinc, andwashing and drying the article.

6; Aproc'ess for metalizing a non-metallic arti-.

cle of the class described which includes the steps of subjecting thearticle to a silver nitrate bath for approximately thirty seconds atroom temperature, drying and subjecting thearticle to an oxidizing bathof water, denatured ethyl alcohol and sodium hydroxide atroom"temperaturefor approximately thirty seconds, drying the-'articleand subjectin the same to a bat-hcontainingzlnc 3 sulphite-forapproximately'two minutes at" room temperature. r

7; A process for metalizing a nommetalllcarticle of the classdescribed'whichincludesthe step of subjecting thearticle to a-solu'tionof cellulose nitrate and-acetone having abOnsis'tencyOI'light cream,drying the articlefsubje'ctingthearticle to a bath ofdenatured'alcoh'ol; ace'tone'and'silver nitrate, drying and "subjectingthe "article "to an oxidizing bath of water, denatured alcohol and analkali metal hydnoxide and drying-andsubjecting the'article to areducing bath oil zinc and sodium-bisulphita H H V H FREDERICK" R O SSW'EN'GER.

REFERENCES- CITED FOREIGN PATENTS V Country, "Date" "GreatBritain 1915anc Ju e; 1.9.2

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